Functionalized elastomer

ABSTRACT

The present invention is directed to a copolymer comprising: a polyisoprene backbone chain with a microstructure comprising grater than 98 percent by weight of cis 1,4 linkages; and polymeric sidechains bonded to the backbone chain, the sidechains comprising a polymer derived from a monomer having a hydrogen bond donor site and a hydrogen bond acceptor site.

BACKGROUND

Polyisoprene is a key material for producing a broad range of consumerand industrial products. The two most common forms for polyisoprene are“natural rubber” and “synthetic polyisoprene”. Natural rubber typicallyis derived from latex produced by Hevea brasiliensis (i.e., the commonrubber tree), although a broad range of other plants (e.g., guayule andTaraxacum kok-Saghyz (aka Russian dandelion)) also are known to producestoichiometrically similar, rubber-like materials. Unlike naturalrubber, which is only formally derived from polymerization of isoprene,synthetic polyisoprene is actually produced by large-scale, industrialpolymerization of isoprene monomer.

The structures of synthetic polyisoprene (PI) and natural rubber (NR)are similar enough to allow for free substitution of either rubber inmany applications, but there are important differences. For example,rubber produced by the rubber tree has a high molecular weight and atendency to crystallize more completely and faster than commerciallyavailable synthetic PI. The high molecular weight is desirable forimparting “green strength” during tire manufacturing. The rapidstrain-crystallization of rubber is believed to be responsible for theexcellent wear and tear properties of natural rubber-especially undersevere conditions.

Early efforts to develop synthetic PI as a replacement for naturalrubber elucidated much of the fundamental technology and allowedcommercialization of synthetic PI to be achieved in the 1960's. (seee.g. Schoenberg, et al Rubber Chem Tech. 52, 526-604 (1979)) In general,the following characteristics are believed to be desirable in syntheticPI intended for tire applications: high cis-content (vs trans content);high 1,4-addition (vs 3,4-addition); high head-to-tail content; and highmolecular weight.

Subsequent efforts to achieve the highest practical level for eachcharacteristic—especially using Neodymium-based Ziegler/Natta-typecatalysts have built upon the early work and led to today's bestsynthetic replacements for NR. (see e.g. Friebe, et al Adv. Polym. Sci.204, 1 (2006))

For several decades, it was believed that the differences betweennatural rubber and synthetic rubber were the result of natural rubberhaving an almost pure cis-1,4 stereochemistry and branched polymer chainstructures. The potential role of non-rubber constituents in naturalrubber was largely ignored. It now appears from extensive recent work byProf. Yasuyuki Tanaka and coworkers that the non-rubber components playan essential role in determining the properties and performance ofnatural rubber. (see e.g., Tanaka, et al Polymer 41, 7483-8 (2000);Rubber Chem. Tech. 74, 355-75 (2001); Biopolymers 2, 1-25 (2001)) Thisis particularly true for Hevea rubber, which clearly has a structurewith nanometer-scale phase domains that can explain many of the propertydifferences between natural rubber and synthetic rubber. In other words,natural rubber is best viewed as a nanostructured elastomer rather thana hydrocarbon polymer with non-hydrocarbon impurities.

SUMMARY

The present invention is directed to a copolymer comprising: apolyisoprene backbone chain with a microstructure comprising grater than98 percent by weight of cis 1,4 linkages; and polymeric sidechainsbonded to the backbone chain, the sidechains comprising a polymerderived from a monomer having a hydrogen bond donor site and a hydrogenbond acceptor site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of stress versus strain for elastomer samples.

FIG. 2 is a graph of stress versus strain for elastomer samples.

DESCRIPTION

There is disclosed a copolymer comprising: a polyisoprene backbone chainwith a microstructure comprising greater than 98 percent by weight ofcis 1,4 linkages; and polymeric sidechains bonded to the backbone chain,the sidechains comprising a polymer derived from a monomer having ahydrogen bond donor site and a hydrogen bond acceptor site.

In one embodiment, the copolymer has the structure of formula IX

Y—Z]_(n)  (I)where X is a polyisoprene having greater than 98 percent by weight ofcis 1,4 linkages;

-   Z is a polymer derived from a monomer having a hydrogen bond donor    site and a hydrogen bond acceptor site;-   Y is a dithiol linking group having the structure of formula II    —S—R—S—  (II)    where S is sulfur and R is a divalent organic group, and one S is    covalently bonded to X through a thioether linkage and the other S    is covalently bond to Z through a thioether linkage; and n is the    number of    Y—Z] groups bonded to X.

Various strategies have been attempted for the synthesis offunctionalized polyisoprene (PI) of formula I which can show increase intensile strength by inducing nanostructure formation thereby mimickingnatural rubber (NR). One objective is to use polyisoprenic polymers withhigh cis-content which would enable the strain induced crystallizationas observed in NR. One chemical route to such synthetic polymersutilizes synthesis of functionalized polyisoprene having groups whichcan exhibit non-covalent intermolecular interactions (e.g. hydrogenbond, Vander Waal's, electrostatic etc.). The most commonly used routefor accessing moderate to high cis-PI are Neodymium polymerization andanionic polymerization. It has now been found that a functionalizedpolyisoprene may be obtained through a sequence of partial epoxidationof high cis polyisoprene, reacting the epoxy groups with amultifunctional coupler such as a dithiol, followed by grafting apolymer derived from a monomer having a hydrogen bond donor site and ahydrogen bond acceptor site to the coupler.

Polyisoprene suitable for functionalization includes high-cispolyisoprenes with cis 1,4 microstructure of greater than 98 percent byweight. Suitable polyisoprenes include synthetic polyisoprenes made bysolution polymerization with Ziegler-Natta catalysts such as a neodymiumcatalyst, and naturally occurring polyisoprene such as guayule rubber.Such polyisoprenes are well known in the art and commercially available.

Functionalization of the polyisoprene to produce the copolymer I may bedone by a multistep synthesis including 1) partial epoxidation of thepolyisoprene X to produce an epoxidized polyisoprene, 2) a ring-openingreaction of the oxirane groups of the epoxidized polyisoprene with adithiol to produce a thiol functionalized polyisoprene, and 3)thiol-enereaction of the thiol functional polyisoprene with athiolophile-functionalized polymer Z derived from monomers having ahydrogen bond donor moiety and hydrogen bond acceptor moiety.“Thiolophile” as used herein refers to a functional group susceptible toreaction with a thiol in a thiol-ene or thiol-yne reaction, as are knownin the art.

Partial epoxidation of the polyisoprene may be accomplished usingmethods as are known in the art. In one embodiment, the polyisoprene issubjected to a peroxidation reaction (Prilezhaev reaction). In thisembodiment, the polyisoprene is reacted with a suitable peroxy acid torandomly convert a fraction of the polyisoprene carbon-carbon doublebonds to oxirane rings as shown in Scheme 1. Suitable peroxy acidsinclude meta-chloroperoxybenzoic acid (mCPBA) and the like.

The partially epoxidized polyisoprene is converted to athiol-functionalized polyisoprene by reacting at least some of theoxirane rings of the epoxidized polyisoprene with a dithiol of formulaHS—R—SH, where R is an organic group. The reaction may be performed inalkaline environment in a suitable solvent such as THF at roomtemperature until achieving the desired degree of functionalization, asshown in Scheme 2.

In one embodiment, R is —[(CH₂)₂—O—]_(k)—(CH₂)₂— where k is an integerranging from 1 to 10 and the dithiol is a polyethylene glycol dithiol.In one embodiment, k=2 as seen in Scheme 2.

In one embodiment, the dithiol attached to the epoxidized polyisopreneranges from 0.001 to 20 percent by weight, based on the weight of thepolyisoprene.

As seen in Scheme 2, the copolymer includes hydroxyl groups resultingfrom the ring opening of the oxirane, and may also include unopenedoxirane groups.

In one embodiment, the polymer Z derived from a monomer having ahydrogen bond donor moiety and a hydrogen bond acceptor moiety includeshomopolymers and copolymers of various monomers, including but notlimited to polymers of: acrylamides and substituted acrylamides,methacrylamides and substituted methacrylamides, acrylic acids andsubstituted acrylic acids, methacrylic acids and substituted methacrylicacids.

The term “hydrogen bond” is used herein in the same manner as would beunderstood by one of ordinary skill in the art. The terms “hydrogen bondacceptor moiety” and “hydrogen bond donor moiety” are defined herein asmoieties that are capable of forming a hydrogen bond when at least oneacceptor moiety and at least one donor moiety are present.

In one embodiment, the polymer Z is a polymer of a monomer of formulaIII

where R⁶ is selected from the group consisting of C2 to C6 linear alkyl,C2 to C6 branched alkyl, and C3 to C6 cycloalkyl.

In one embodiment, Z is of formula (IV)

where R⁷ is selected from the group consisting of C2 to C6 linear alkyl,C2 to C6 branched alkyl, and C3 to C6 cycloalkyl.

In one embodiment, the polymer Z is a polymer of an N-substitutedmonoalkyl acrylamide derivative.

In one embodiment, the polymer Z is a polymer of N-isopropylacrylamide.

In one embodiment, the polymer Z has a weight average molecular weightranging from about 500 to about 20000 g/mol.

In one embodiment, the copolymer comprises from about 1 to about 20weight percent Z.

The copolymer of formula I may be produced by various methods. In oneembodiment, the copolymer may be produced by functionalizing the polymerX with the polymer Z to produce a graft copolymer with an elastomerbackbone X and pendant Z. A convenient way for the functionalization ofa variety of elastomers is the thiol-ene reaction during which anunsaturated carbon-carbon bond present in an appended functional group(the thiolophile) of the polymer Z reacts with a thiol to form athioether. For example, an alkene moiety being present in the maleimidegroup of a maleimide terminated polymer Z may act as the thiolophile. Inorder to allow the functionalization of the polymer X, an in-chainthiol-functionalized version of the polymer X is used.

Various thiolophile-functionalized versions of the polymer Z may beused. Suitable thiolophile groups include but are not limited tomaleimido groups, allylic groups, and alkynyl groups. In one embodiment,a maleimido-functionalized N-isopropylacrylamide polymer (PNIPAM) isused as available commercially from Aldrich. Both mono- and bismaleimidofunctionalized PNIPAM may be used, as are known from Li et al, J. Polym.Sci. Part A, 46 (2008), 5093. Allylic- and alkynyl-functionalizedversions of PNIPAM are also known from Yu et al., J. Polym. Sci. Part A47 (2009) 3544.

The polymer X having pendant thiol groups may be reacted with themaleimide-terminated polymer Z in a thiol-ene reaction to form thecopolymer as illustrated in Scheme 3, where the polymer Z is shown asmaleimide-terminated PNIPAM, poly(N-isopropylacrylamide).

The end-functionalized copolymer of formula I may be compounded into arubber composition.

The rubber composition may optionally include, in addition to thefunctionalized polymer, one or more rubbers or elastomers containingolefinic unsaturation. The phrases “rubber or elastomer containingolefinic unsaturation” or “diene based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (including cis1,4 polybutadiene), polyisoprene (including cis 1,4 polyisoprene), butylrubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3 butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polyisoprene (natural or synthetic), polybutadiene andSBR.

In one aspect the at least one additional rubber is preferably of atleast two of diene based rubbers. For example, a combination of two ormore rubbers is preferred such as cis 1,4-polyisoprene rubber (naturalor synthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3 butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil.Processing oil may be included in the rubber composition as extendingoil typically used to extend elastomers. Processing oil may also beincluded in the rubber composition by addition of the oil directlyduring rubber compounding. The processing oil used may include bothextending oil present in the elastomers, and process oil added duringcompounding. Suitable process oils include various oils as are known inthe art, including aromatic, paraffinic, naphthenic, vegetable oils, andlow PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.Suitable low PCA oils include those having a polycyclic aromatic contentof less than 3 percent by weight as determined by the IP346 method.Procedures for the IP346 method may be found in Standard Methods forAnalysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr ofsilica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm3/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), crosslinked particulate polymer gels includingbut not limited to those disclosed in U.S. Pat. Nos. 6,242,534;6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment the rubber composition may contain a conventionalsulfur containing organosilicon compound. In one embodiment, the sulfurcontaining organosilicon compounds are the 3,3 bis(trimethoxy ortriethoxy silylpropyl)polysulfides. In one embodiment, the sulfurcontaining organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and/or 3,3bis(triethoxysilylpropyl)tetrasulfide.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140 C and 190 C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100 C to 200 C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110 C to 180 C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

EXAMPLES

Reagents

Dichloromethane (DCM), tetrahydrofuran (THF), methanol (MeOH),triethylamine (Et₃N), meta-Chloroperoxybenzoic acid (mCPBA), LithiumHydroxide (LiOH), and maleimide-functionalizedPoly(N-isopropylacrylamide) (Maleimide-PNIPAM) were purchasedcommercially from Sigma-Aldrich and used as received without any furtherdistillation/purification treatment. 2,2′-(Ethylenedioxy)diethanethiol(dithiol, DTH) were also purchased from Sigma-Aldrich and dried overmolecular sieves before use. High cis-Neodymium Polyisoprene (Nd—PI) wassynthesized using standard Neodymium polymerization as disclosed forexample in U.S. Pat. No. 6,780,948. The Nd—PI prepared for this work hasa cis-content of greater than 98%.

Instruments:

-   -   a) Nuclear Magnetic Resonance (NMR): ¹H NMR spectra were        recorded on a Varian INOVA 400 MHz spectrometer. Chemical shifts        are given in parts per million (ppm) either by using        tetramethylsilane (TMS, δ=0.00) or the residual protic solvent        peak (for CHCl₃, δ=7.26 and for CH₂Cl₂, δ=5.30) as a shift        reference for ¹H NMR spectra.    -   b) Tensile Testing: Physical testing of the solution cast        polymer films were done on a MTS Tensile Tester with 100 N load        cell. Engineering strain rate of 10%/s was applied to each        samples which corresponded to a displacement rate of 2.6 mm/s.    -   c) Gel Permeation Chromatography (GPC): GPC analysis was done        using Agilent 1100 Series-LC with a Wyatt Technologies MiniDawn        detector and Gilson 234 Auto sampler. THF was used as the mobile        phase at a flow rate of 1.00 mL/min at a column temperature of        35° C. Astra 4.73.04 software was used for analysis of the        chromatogram and determining calculated sample mass, molecular        weight (Mw, Mn) and polydispersity (PDI=M_(w)/M_(n)).

Reaction System:

-   -   For all reactions, the polymer was charged into the reaction        vessel (typically a round bottom flask or a reactor) and the        solvent was added to dissolve the polymer. All reactions were        performed under nitrogen just as a routine practice and not as a        stringent requirement. Unless otherwise stated, the reactions        are carried out at room temperature (rt).

Example 1

To a 250 mL DCM solution of Nd—PI (5.2 g, 7.6 e⁻² mols) at 0° C. wasadded a DCM solution (4 mL) of mCPBA (0.0188 g, 8.39 e⁻⁵ mols, 77% puremCPBA) targeting a 0.11% epoxidation level. The reaction mixture wasstirred at 0° C. for 6 hours. At the end of this time, the polymer wasisolated and purified by precipitation in methanol. ¹H NMR analysis ofthe polymer showed the appearance of new resonances at δ 2.69 ppm, δ1.57 ppm, and δ 1.29 ppm corresponding to the epoxide formation.Calculation based on the ¹H NMR integrals of the protons attached to theepoxydized and unepoxidized carbon-carbon double bonds indicated 0.11%epoxidation of the polymer backbone of Nd—PI. The epoxide groups arerandomly distributed along the polymer chain rather than as a block.

Guayule Rubber (coagulated) was also successfully epoxidized using thechemistry described in Example 1. Table 1 summarizes the results of thesynthesis of epoxidized elastomers with various mol % of epoxidationlevels.

TABLE 1 Sample M_(w)(kDa) Polymer % cis-content % Epoxidized^(a) 1 ~1000Nd PI >98 10 2 ~1000 Nd-PI >98 0.22 3 ~1000 Nd-PI >98 0.11 4 ~1000Nd-PI >98 0.05 5 ~950 Guayule >99 10 6 ~950 Guayule >99 0.11 ^(a)Targetepoxidation = actual epoxidation as monitored by ¹H NMR

Using the appropriate molar % of mCPBA, this route could be efficientlyused for achieving any desired level of epoxidation (0.001 mol % to 100mol %) on any polymer containing a terminal or internal diene. The samereaction can also be done at any temperatures ranging from −78° C. tothe boiling temperature of the solvent used. The rate of reaction wouldvary with the temperature of the reaction e.g., at room temperature thereaction proceeds to completion in less than 1-15 minutes in mostsolvents. Other solvents such a THF, hexanes, benzene, and otheraliphatic or aromatic solvents could also be used successfully as thereaction media. A co-solvent could also be used in cases when the mCPBAis not soluble in the polymer solution.

Example 2

Epoxidized Nd—PI (5.3 g, 8.55 e⁻⁵ mols epoxy groups) was dissolved in100 mL of THF in a round-bottom flask at room temperature. LiOH (0.02 g,8.56 e⁻⁴ mols with respect to epoxy groups) was added to the solutionfollowed by the addition of 2,2′-(Ethylenedioxy)diethanethiol (dithiol,DTH) (0.16 g, 8.56 e⁻⁴ mols with respect to epoxy groups). The reactionmixture was stirred at rt for 24 hours. At the end of this time, thepolymer was isolated and purified by precipitation in methanol. ¹H NMRanalysis of the polymer showed the appearance of two very characteristicresonances: a multiplet at ˜δ 3.63-δ 3.71 ppm corresponding to the‘ethylenedioxy’ groups and another multiplet at ˜δ 2.70-δ 2.72 ppmcorresponding to the —CH₂— attached to the terminal SH-atom connected tothe polymer backbone at the point of the ring-opened epoxide.

Example 3

Ring-opened epoxidized Nd—PI (5.3 g, 8.55 e⁻⁵ mols of pendant thiol) wasdissolved in 250 mL of THF in a round-bottom flask at room temperature.To this solution was added a THF solution of Maleimide-PNIPAM (0.86 g,3.42 e⁴ mols) followed by the addition of excess Et₃N. The reactionmixture was stirred for 5-15 min at room temperature. At the end of thistime, the polymer was isolated and purified by precipitation inmethanol. Gel Permeation Chromatography (GPC) analysis was performed toconfirm the quantitative removal of the unreacted Maleimide-PNIPAM fromthe product copolymer. The ¹H NMR resonances assigned to the maleimideprotons at δ 6.69 ppm disappeared and a new resonance appeared at δ 4.03ppm corresponding to the —CH— of the isopropyl group of theMaleimide-PNIPAM. The reaction yield was quantitative. Thismaleimide-PNIPAM grafted product copolymer of 1 MM Nd—PI has an averageof maximum 0.11 mol % PNIPAM grafted on each polymer chain.

Example 4

Tensile testing was done on maleimide-PNIPAM grafted product copolymerof 1 MM Nd—PI synthesized in Example 3. A solution-based film of themaleimide-PNIPAM grafted product copolymer was casted and the solventwas allowed to evaporate completely. The tensile test data of the driedcast-film is shown in FIG. 1. The control for comparison of the tensilestrength was the unfunctionalized 1 MM Nd—PI. As can be seen from FIG.1, the maleimide-PNIPAM grafted product copolymer of 1 MM Nd—PI (1) hasa tensile strength significantly higher than the controlunfunctionalized 1 MM Nd—PI (2). GPC of the product copolymer showedthat the molecular weight is around 1 MM, which indicated that nochemical cross-link occurred during the reaction. Hence the increase intensile strength of the green polymer is purely due to intermolecularnon-covalent interaction between the in-chain grafted maleimide-PNIPAMgroups.

Tensile testing was also performed on solution cast film ofmaleimide-PNIPAM grafted copolymer of Guayule rubber (M_(w) of Gualyulerubber is approx 950 kDa). The tensile test data of the dried cast-filmis shown in FIG. 2 It can be seen that the in-chain grafting of PNIPAMon Guayule (3) significantly increased the tensile strength of theGuayule rubber as compared with unfunctionalized Guayule rubber (4). Allthe tensile testing was done on “green or uncured” polymers.

What is claimed is:
 1. A copolymer comprising the structureX

Y—Z]_(n) where X is a polyisoprene; Z comprises a polymer derived from amonomer having a hydrogen bond donor site and a hydrogen bond acceptorsite; Y is a dithiol linking group comprising the structure—S—R —S— where S is sulfur and R is a divalent organic group, and one Sis covalently bonded to X through a thioether linkage and the other S iscovalently bond to Z through a thioether linkage; and n is the number of

Y—Z] groups bonded to X, wherein n ranges from about 2 to about
 30. 2.The copolymer of claim 1, wherein Z comprises a polymer derived from amonomer of formula

where R⁶ is selected from the group consisting of C2 to C6 linear alkyl,C2 to C6 branched alkyl, and C3 to C6 cycloalkyl.
 3. The copolymer ofclaim 1, wherein Z is selected from the group consisting ofpoly(N-isopropylacrylamide) and poly(N-cyclopropylacrylamide).
 4. Thecopolymer of claim 1, wherein the polymer Z has a weight averagemolecular weight ranging from about 500 to about 20000 g/gmol .
 5. Thecopolymer of claim 1, comprising from about 1 to about 20 weight percentZ.
 6. The copolymer of claim 1, wherein Z comprises a polymer of formula

where R⁷ is selected from the group consisting of C2 to C6 linear alkyl,C2 to C6 branched alkyl, and C3 to C6 cycloalkyl, and m is the degree ofpolymerization of the hydrocarbon chain.
 7. The copolymer of claim 1,wherein Z further comprises a terminal maleimide group covalently bondedto a sulfur of Y.
 8. The copolymer of claim 1, wherein Y is derived froma polyethylene glycol dithiol.
 9. The copolymer of claim 1, wherein R is—[(CH₂)₂—O—]_(k)—(CH₂)₂ —where k is an integer ranging from 1 to
 10. 10.The copolymer of claim 1, wherein R is —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—. 11.The copolymer of claim 1, wherein the polyisoprene comprises amicrostructure comprising grater than 98 percent by weight of cis 1,4linkages.
 12. The copolymer of claim 1, wherein the polyisoprenecomprises hydroxyl groups.
 13. The copolymer of claim 1, wherein thepolyisoprene comprises oxirane groups.
 14. A rubber compositioncomprising the copolymer of claim
 1. 15. A pneumatic tire comprising therubber composition of claim 14.